Photographic exposure determining device



y 1950 K. w. WENNERSTROM 2,508,129

PHOTOGRAPHIC EXPOSURE DETERMINING DEVICE Filed Feb. 15, 1949 2Shet$Sheet 1 INVENTOR KNUT W WEN/VERST/POM BY +(M I ATTORNEYS May 16,1950 K. w. WENNERSTROM 2,508,129

PHOTOGRAPHIC EXPOSURE DETERMINING DEVICE Filed Feb. 15, 1949 2Sheets-Sheet 2 INVENTOR KNUT l4. WENNERSTROM F M M ATTORNEYS PatentedMay 16, 1950 UNITED STATES PATENT OFFICE PHOTOGRAPHIC EXPOSUREDETERMINING DEVICE Knut W. Wennerstrom, Dayton, Ohio ApplicationFebruary 15, 1949, Serial No. 76,550

This invention relates to a photographic exposure determining device,and more particularly, to a device which gives the photographer a visualindication of the exact tone or density which will result in thefinished positive print by the use of a, particular exposure. By"particular exposure is meant a given aperture opening and exposuretime, or any set of different aperture openings and exposure times whichwould result in the same amount of light reachingthe film when thepicture is taken.

Most photographers are familiar with the usual types of scales which areavailable for use, with or without the assistance of light measuringdevices, in determining the correct exposure for a given scene. In mostof these devices, once a light brightness value is determined, a datummarking on a dial is moved to a position adjacent the light value found,resulting in the alignment of a series of f opening values and a seriesof exposure times. The desired exposure can then be selected from any ofa group of alternative combinations of 1' opening and exposure time.

In arrangements of the type Just described, the location of the datummarking on the dial is a mere approximation of average operatingconditions for the average type of scene, and in many cases theparticular position of this marking is at variance with the practices ofthe photographer. That is, because of the particular habits and type ofequipment and developing facilities and techniques used by thephotographer, use of the meter in strict conformity withthe'manufacturers directions results in pictures which vary in tone ordensity from that of the scene photographed, and/or from the particulartone or density desired by the photographer. This variance can becorrected either by a change in the techniques practiced by thephotographer in the darkroom or by the making of a mental correction intheindication given by the meter so as to compensate for theinaccuracies or variances known to result from strict use of the meterin accordance with the manufacturer's recommendations.

In one type of meter now in common use, the marking referred to above isaccompanied by two other markings, one on each side of the normalmarking. These other two markings indicate, respectively, one-half anddouble exposure, and one or the other of these extra markings may belined up with the light value reading when it is de sired to halve ordouble the exposure. However, even by the use of these extra markings,the photographer is still working mainly by guess, and hehas no accurateway of determining, at the time 8 Claims. (Cl. 23564.7)

he takes the picture, whether or not his finished positive print willcorrespond in the manner which he desires, to the scene photographed.

The present invention overcomes all of the dis- .advantages pointed outabove by providing a graduated set of positive areas of graduateddensity from black to white, for direct comparison with the scene beingphotographed, and in a preferred embodiment of the invention, this scaleof densities is mounted on the dial of the exposure determining devicein such a manner that the photographer, at the time he is ready to takea picture, can select the tone or density area matching the desiredtonal density of the finished print, and the selected density area canthen be aligned with the light value reading, instead of aligning a merearbitrary marking as in the general practice described above. Thephotographer may match one of the areas of the density scale with aparticular portion of the scene being photographed so as to reproducethat particular portion of the scene most faithfully, or he maypurposely select a different shade, knowing that the final print willthenhave the tone and density of the selected density scale area, ratherthan the exact tone and density of the scene photographed. The use ofthe invention is of course based on the assumption that the photographerusing the device has a standardized darkroom technique so that nounwanted variations will be introduced during the developing or printingoperations.

. The device which I have invented may also in-' clude a color rangesection, separately calibrated for use when taking photographs in color.While I have found that best results are obtained by using ninevariations of density between black and white for use in black and whitephotographs, it is usually preferable to limit the range of shades inthe color photography section to the five or six shades falling aboutand on the light side of the central portion of the density range usedfor black and white photography. This results from the fact that thelatitude of color film is considerably smalleror narrower than that ofblack and white film, and also from the fact that subjects fallingwithin the darker end of the black and white range will have too low areflectance to hold up in color when final color prints are made. Thecolor range section permits the photographer to make sure that hisexposure is correct for the particular color in the scene which is to bereproduced most accurately in the final print.

An object of my invention is to provide an exposure determining deviceby the use of which a photographer can compare a graduated range oftonal densities with the scene being photographed, and by selecting aparticular tonal value which he wishes to reproduce in the finishedpositive print, can utilize this density value in selecting the 1opening and exposure time which he will use in taking the picture.

Another object of the invention is to provide a device for attachment tothe dial of a photographic exposure determining device, and by means ofwhich, a tonal density corresponding to the density of the finishedpositive print can be compared with the scene being photographed, andcan be used in selecting the dial setting'of the indicating device.

Another object of the invention is the provision on a photographicexposure determining device of a tonal density scale graduated betweenblack and white, so that this scale can be compared directly with thescene being photographed. and the desired tonal density can be alignedwith the light brightness indication of the scene, thereby lining up thevarious f opening numbers with the corresponding correct exposure timeson the device.

A further object of the invention is the provision of a device asdescribed in the preceding object, which includes density indicationsparticularly designated for comparison with a scene being photographedin color.

Still another object of the invention is to provide a device asdescribed in the various preceding obiects of the invention, and whichcan be readily attached to and adjusted on the dials of various types ofexposure devices.

These and other objects of the invention will become more apparent froma study of the following specification, taken in coniunction with theaccompanying drawings, in which:

Fig. 1 is a face view showing one form of the invention in use on anexposure determining device;

Fig. 2 is a face view of the scale shown in Fig. 1 and in a form whichcan readily attached to and detached from the dials of an exposuredetermining device;

Fig. 3 is an edge-on view of the device shown in Fig. 2, and

Figure l is a face view of a modified form of the scales shown in Figure2.

Referring now to the drawing in more detail, Fig. 1 shows what is, forthe most part, a conventional exposure determining device as used withthe popular Weston Universal exposure meter Model. 715. This device hasa stationary outer scale it bearing a plurality of light brightnessindicating numbers, the larger numbers indicating increasing lightbrightness. Spaced inwardly from the set of light indications I5), is astationary set of numbers H which correspond to the emulsion speeds ofvarious types of films. The film speeds It may be viewed through awindow 52 in a movable dial plate l3 which is mounted above thestationary base which carries the light indications l0 and the filmspeed values ii. The dial l3 maybe locked in a plurality of noneselected in accordance with the par ticular film used, by means of aspring device H1. The fiat dial I3 carries about its peripheral portiona series of exposure time values shown at iii. Still another fiat dialI6 is mounted on top of dial l3, and coaxially therewith. The dial 56has two semi-circular positions having different radii. The portion ofsmaller radius has a plurality of f opening numbers I! printed orotherwise placed thereon, so as to be moveable in close proximity to theexposure time values it": carried on the dial IS. The dial l6 has anarcuate window iii to permit viewing oi the film speed values I l.

iai plate 15, which is moveable freely with respect to the otherportions of the device, ordinarily carries at some point along the edgeof its portion of larger radius, a marking usually in the form of anarrow (not shown), which, when moved to a position adjacent any one ofthe light indication values it. so positions the late iii that thevarious f opening numbers l! are positioned adjacent the correspondingexposure time values I5 for that particular light brightness. However,according to the present invention, a fan shaped tonal scale 20 ismounted on the dial E5 on the portion of greater radius so as to coverup or replace the conventional arrow or other marking which wouldordinarily be found thereon.

The tonal scale shown in Fig. l is shown in greater detail in the otherfigures of the drawand particularly in Fig. 2, and since the scale shownin Figs. 2 and 3 differs from that of 1. only in the manner ofattachment to the dial plate it, the scale will be described in greaterdetail in connection with the figures showing greater detail. As shownin Fig. 1, the scale 20 is attached to the dial plate I6 by means of awasher or retainer 2| held in place by a screw or bolt 22 which passesthrough the center and pivot of the dial arrangement. The scale 2i inthis embodiment is also secured to the dial plate !6 by means ofadhesive but in view of the disclosure below, the invention is not to belimited to this manner of attachment.

Referring now to Figs. 2 and 3, the fan shaped scale 28 has a centralmounting portion 25 by which it is attached to the meter by screw 22a.The bolt 22a is threaded into an opening (not shown) as explained inconnection with Fig. l, and once the correct position of the scale 26 isdetermined, it may be promptly attached to the dial. l 6 by means ofadhesive, or it may be caused to revolve with plate 16 by means of africtional material 28 carried on the undersurface of the scale as shownat 25 in Fig. 3.

Figs. 2 and 3 also show in dotted lines other alternate means ofattachment of the scale to the plate l6, although it will be readilyunderstood that various additional types of attachment may be usedwithout departing from the inventive concept. As shown in dotted lineson Figs. 2 and. 3, spring clips 21 may be positioned about the peripheryof the scale at spaced points so as to clip under the outer edge ofplate I6. In another variation, tabs 28 may be provided on the radiallyextending marginal portions of the scale, and by means of small screws29 passing through slots 30 in these tabs for engagement with threadedopenings (not shown) in plate the scale 28 may be mounted in variousrotational positions on the plate 16 so as to suit the individual usersneeds.

Most of the face area of the scale 20 is taken up with a plurality ofareas 35 of graded density run or from white at 350. to black at 35b,and sepe. by thin lines 36. I have found it con lute-d to the use ofthis'particular number,

for convenience, by a series of numbers 31 beginning with the areas nextto the black area. 3512.

For use when taking photographs in color, the scale 20 has a portion ofthe areas of varying densities 35 coordinated with a set of numbersshown at 40 in Fig. 2, these numbers being placed adjacent certain ofthe areas 35 near the central portion and on the bright side of thescale 35. The numbers of the color scale as shown at 40 are groupedtogether more closely than the numbers 3'! designating the areas 35 ofthe black and white scale. The smaller latitude of color films is thereason for the arranging of the number 40 for color work in the mannerillustrated.

The device is used in the following manner:

The light brightness of the scene or subject to be photographed isdetermined. The photographer then appraises the scene itself, or theimage on the ground glass, whichever he prefers, he then selects abracket of about four or five shades 35 which seem approximately tomatch the "Major Area of the scene. He then places the center of thatbracket of shades at the exact spot or number on the light value scaleIt indicated when the reading was taken, thereby automatically placingthose shades or values in the scene, in their proper position in regardsto the density range of the film, in other words the film latitude. Theproper speed for each i stop can now be obtained from the shutter speedscale l3. The thin lines 36 located half between each shade area 35 onthe device are to be used when the center of a bracket falls between twoshades 35, and also when individual readings are taken oi a subject,whose value appears to fall between two shades of the device.

On indoor setups, where the photographer has control of the lighting, hemay take individual readings of the subjects to be photographed, firsttaking a reading of the most important subject, then selecting the shade35 on the device which appears to match, setting that shade at thecorrect value on the light value scale when the reading was taken, thenby leaving this shade in position, he may proceed to check othersubjects in the scene by taking individual readings of each one. Bywatching the results of each reading, he can in each operation, checkwith the shades on the device, and see approximately how each subjectwill look in the final print. If any change in lighting seems necessary,the photographer can move his lights, and then by rechecking with thedevice, see just what results each alteration in his lights produced.Ail of this can be done before the exposure is made, thus eliminatingany disappointing results in the final. print. On outdoor close-upswhere the photographer has no control of the light source, he may attimes, when unusual or special afiects are desired, deliberately selecta shade or two, or even more to the dark or light side of the shadewhich matches the subject. The device will in each case adjust theexposure time to give the right density in the negative to reproduce theshade selected, when the final print is made.

Since the position of scale 2i! is adjustable on the exposure guide dialby the means described above, the photographer can adjust the scale 23by rotation to the left or the dark end relative to plate l6 shouldconditions such as shutterspeed variances, types of developer, etc.,cause negatives constantly to come up underexposed or too thin. Sincethe shades progress from left to right, each shade to the right or lightend represents a measured increase in negative density, so the scale 20should be rotated about its center to the left, thereby bringing thenext lighter shade into the position previously occupied by the area toits left, or shifting two shades to the left if necessary, until thedesired results are obtained. If consistent overexposure occurs, theprocess is reversed by shifting to the right, as each dark value broughtinto position represents a measured decrease in negative density. If thephotographer uses several types of developers, the device is best leftin normal position, making adjustments by simply moving the wholeexposure guide dial one or more shades to the left or right, dependingon what type of developer is going to be used. The photographer should,after making a few experimental tests, be able to decide thefinal'position of the scale 20 on the exposure guide dial of his meter,to coordinate with his own individual dark room practices. A card with aset of shades corres ponding to shades (in the scale 20 may be used bythe amateur until he acquires proficiency in comparing the shades on thescale 35 with the actual subjects of which he is taking light readings,after which he will rely entirely on the scale 35 mounted on the meter.It should be remembered that the accuracy of the device in determiningfinal print results is dependent on the time and temperature of thedeveloper used during the experimental tests, as well as the type ofdeveloper used. All these must be kept constant, as changing from onedeveloper to another can produce more or less density in the negativeeven though the time and temperature is the same, and thereby making itnecessary to do some manipulating when the final prints are made.

It should now be apparent that I have invented a simple yet highlyefiicient device which facilitates the selection, for every picture, ofa set of exposure conditions which will give the exact tonal densitydesired in the finished picture. My invention is susceptible of so manyvarious embodiments without departing from the inventive concept that itwould needlessly increase the length of this specification to attempt toenumerate all such variations. However, it should be understood that thescale of gradations can be continuous and can be used in accordance withmy invention, either with an exposure indicating device mounted on alight meter, or it can be used with such a device separate from themeter, it being important only that the exposure indicating device he ofthe type in which ordinarily a marking is matched with, that is, movedto a position adjacent an indication of the brightness of the light. Byusing a graduated scale of densities in place of the ordinary marking insuch a device, my invention in practice achieves the aforesaidadvantages.

Another variation which might be used would be to have two sets of thevarying density areas 35 positioned one radially outwardly of the other,and with the densities of the two sets varying in opposite directions,one becoming darker in a counter clockwise direction as in Fig. 2 andindicating tonal density of the finished print, and the other becomingdarker in the clockwise direction and indicating tonal density of thenegative, as shown in Figure 4.

I also wish to point out that the manner oi attachment ofscaie ZO tothe-indicating device is not critical as longas the scale can be fixedin at least one position on the structure corresponding to plate IS onthe Weston device described above, it being preferable that the posi*tion of the scale can beyaried until the best position for eachparticular user is determined.

I claim:

1. In a photographic exposure determining de-. vice of the type in whicha datum marking cooperates with a series of light brightness indiecations to indicate correct exposure conditions, that improvement inwhich said datum marking comprises a graduated series of tonal densityareas for direct comparison with the scenebeing photographed andselection of an area having a density corresponding most nearly to theden sity desired in the positive print, each of said being substantiallyidentical in tonal den sity with the density which standardizeddeveloping conditions will produce in a positive print resulting from anexposure made under exposure conditions selected by aligning the area ofdesired density with the light brightness indication given by thescene.-

2. An arrangement as set forth in claim 1, and indicia means fordistinguishing certain of said areas for photography in color.

3. An arrangement as set forth in claim 1, a flat element carrying saidareas and adapted for convenient attachement to conventional typeexposure determining devices, and means for attaching said element.

4. An arrangement as set forth in claim 1, a flat element carrying saidareas and adapted for convenient attachment to conventional types ofexposure determining devices, and means for attaching said element, saidattaching means including means for adiustably positioning said elementto permit selection of a permanent position best suited to varyingphotographic technidues.

15. An arrangement as set forth in claim 1, a flat element carrying saidareas, and spring clips on said element for mounting said element on thedevice.

6. An arrangement as set forth in claim 1, a

fiat element carrying said areas, and slotted tabs carried by saidelement to faciiltate attachment to the device.

'7. An arrangement as set forth in claim 1, and a flat, fan-shapedelement carrying said areas, a central portion of said element beingprovided with a mounting opening.

8. In a photographic exposure determining device of the type in which adatum marking cooperates with a series of light brightness indicationsto indicate correct exposure conditions, that improvement in which saiddatum marking comprises a graduated series of tonal density areas fordirect comparison with the scene being photographed and selection of anarea having a density corresponding most nearly to the density of aportion of the scene being photographed, each of said areas beingsubstantially identical in tonal density with the density whichstandardized developing conditions will produce in a positive printresulting from an exposure made under exposure conditions selected byaligning the area of desired density with an indication bearing a knownrelation with the light brightness indication given by the scene.

KNUT W. WENNERS'IROM.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,322,044 McFarlane et al. June15, 1943 2,323,676 Rath June 6, 1943 24,380,244 Jones et a1 July 10,1945 2,408,944 Miller Oct. 8, 1946

